1. Field of The Invention
The present invention relates generally to a fuel-purging system used for a fuel processing system which processes vaporized fuel in a fuel tank before the fuel is introduced into an internal combustion engine for automotive vehicles. More specifically, the invention relates to a self-diagnosable fuel-purging system which can detect abnormality in itself.
2. Description of The Background Art
Conventionally, in fuel-purging systems used for fuel processing systems which process vaporized fuel within a fuel tank, when the pressure within the fuel tank reaches a positive pressure greater than a predetermined value, the vaporized fuel within the fuel tank is introduced into a canister to be collected therein, and then the fuel collected in the canister is supplied to an engine through a purging passage.
The purging passage is provided with a diaphragm valve controlled to be opened and closed in accordance with negative throttle pressure. The diaphragm valve is suitably controlled so that fuel-purging may be performed.
When the engine is driven in an idling condition, or stopped, the diaphragm valve is caused to close so that purged fuel is prevented from being supplied to the engine. In this way, the air/fuel ratio of exhaust gas from the engine is prevented from becoming too rich, so that, for example, starting operation of the engine becomes impaired. Such a condition will be hereinafter referred to as "fuel-purging prevented condition". Such a system is described in Japanese patent Second (examined) Publication (Tokko Sho.) No. 53-19729.
However, the aforementioned conventional fuel-purging system does not have a system or program for determining whether or not the fuel-purging system is functioning normally, and can not detect abnormality in the fuel-purging operation itself.